1. Field of the Invention
The present invention relates to a unit housing structure in an electronic device provided with a guide structure for smoothly guiding a detachable unit portion to a predetermined position in a unit mounting portion.
2. Description of the Related Art
In an electronic device composed of a plurality of printed boards packaged on a shelf, for example, in a communication apparatus, heat generation from the printed boards is a problem. Structure for emitting the heat outside is therefore employed. Commonly employed as this cooling method is forced air cooling using a fan. The fan has a certain life expectancy, but may encounter trouble prior to the expiration of its known life expectancy. For facilitating maintenance and replacement, therefore, it is a common practice for a fan unit to be structured to be detachable from the front side of a unit mounting portion in the body of a device.
Furthermore, since the fan unit needs to supply power or transmit an alarm signal or the like when the number of revolutions of the fan is reduced, the unit requires electrical connection with the device side. The fan unit and the unit mounting portion of the device are therefore both designed to have a connector through which the fan unit and the unit mounting portion are electrically connected.
In addition, for reliably connecting the connectors, the fan unit should be guided such that the connectors face each other while positioned with respect to each other. For this guiding, a guide rail with a groove for guiding is disposed on the side of the unit mounting portion.
Commonly used as this guide rail is a rail having a U-shaped slot whose opposite sides rise vertically to the bottom surface (hereinafter, referred to as a U slot). The fan unit is guided by engaging a guided portion on the fan unit side with this U slot and sliding the guided portion within the U slot. Here, between the U slot of the guide rail and the guided portion of the fan unit, "the width of the U slot is greater than the width of the guided portion" holds and the two are designed to have a little clearance therebetween.
It is ideal that insertion or extraction of the fan unit into or from the unit mounting portion is conducted while keeping the U slot of the guide rail and the guided portion of the fan unit in parallel to each other at any time.
Among modes of a fan unit are a mode of laterally mounting a plurality of fan units each having a few fans so as to meet cooling design or a design concept of an electronic device and a mode of mounting a fan unit large in breadth having numbers of fans thereon. In either mode, for guiding a fan unit large in breadth by a U slot of a guide rail, operating the U slot of the guide rail and a guided portion of the unit while constantly keeping them in parallel with each other is difficult and the unit is highly likely to slant with its left side or right side projecting forward. As a result, an apparent width of the guided portion of the fan unit equals or exceeds the width of the U slot of the guide rail, whereby the guided portion of the fan unit will be pressed against the inner wall surface of the U slot to hitch halfway in the insertion or extraction.
In a case where a right and left slant is to be corrected for rectifying this state, when the amount of rectification is too large, a right and left slant reverse to that before will cause a hitch. Insertion and extraction are highly likely to be conducted through the repetition of this movement to rock the unit leftward and rightward alternately in the traveling direction and cause a hitch. This tendency is more enhanced as the breadth of the fan unit is increased.
Under these circumstances, there is a demand for a unit housing structure provided with a guide structure which enables smooth insertion and extraction without a hitch caused by rocking from side to side.
FIGS. 11 and 12 show one example of a conventional housing structure and FIG. 11 is a perspective view showing a broken-out section of a part of the schematic structure of the housing structure and FIG. 12 is an expanded sectional view taken along line B--B of FIG. 11. More specifically, shown are one example of a fan unit 110 large in breadth having a plurality of fans 175 provided thereon and a fan unit mounting portion 120 in which the fan unit 110 is to be mounted. Although not shown, the fan unit mounting portion 120 is disposed within an electronic device such as a communication apparatus.
In more detail, the fan unit mounting portion 120 has a connector 130 for the connection with the fan unit 110. The connector 130 is connected to the inside of the electronic device by a cable to allow power supply to the fan unit 110 or detect an alarm signal or the like generated from the fan unit 110 due to the reduction of the number of revolutions of the fan. On the left side on cross-beams 180 and 190 of the fan unit mounting portion 120, a guide rail 140 for guiding the fan unit 110 is provided. The guide rail 140, as illustrated in FIG. 12, forms a U slot 170 having its wall surfaces rising perpendicularly to the bottom surface by which the U slot 170 guides the fan unit 110.
On the other hand, the fan unit 110 has a connector 150 at a position opposed to the connector 130 of the fan unit mounting portion 120. In addition, the lower edge of the side surface of the fan unit 110 projects to become a guided portion 160 which will be guided while being fit in the U slot 170 of the guide rail 140. Here, the width of the U slot 170 of the guide rail 140 has a dimension with a little clearance with respect to the board thickness of the side surface of the fan unit 110, that is, the width of the guided portion 160.
Next, operation at the conventional housing structure will be described. First, set the guided portion 160 of the fan unit 110 to the U slot 170 of the guide rail 140 to insert the fan unit 110 into the fan unit mounting portion 120. Insertion is enabled without any problem by inserting the fan unit 110 straight on, with the U slot 170 of the guide rail 140 and the guided portion 160 of the fan unit 110 maintained in parallel to each other at any time by keeping a balance between right and left.
Once the balance between right and left is lost and the fan unit 110 slants, for example, as illustrated in FIG. 13, the guided portion 160 slants to the utmost within the U slot 170 of the guide rail 140, resulting in having the apparent width of the guided portion 160 equaling or exceeding the width of the U slot 170 of the guide rail 140. As a result, the guided portion 160 of the fan unit 110 is pressed against the inner wall surface of the U slot 170 to cause a hitch halfway in the insertion of the fan unit 110.
Here, at the time of correcting the right and left slant by pushing the left side, as one faces it, of the fan unit 110 in order to rectify the slant state, if the amount of rectification is too large, a right and left slant reverse to that of FIG. 13 is generated, for example, as illustrated in FIG. 14 to cause a hitch. Repetition of this movement will result in insertion with the unit rocking rightward and leftward in the traveling direction.
As described in the foregoing, a conventional structure for guiding a unit large in breadth by means of a guide rail having a U slot involves rightward and leftward rocking in the traveling direction to cause a hitch, making mounting of the fan unit difficult. This tendency is more enhanced when the guide rail 140 of the fan unit mounting portion 12 and the guided portion 160 of the fan unit 110 are both made of metal for maintaining the ground potentials of the fan unit mounting portion 120 and the fan unit 110 to be the same than that when either the guide rail 140 or the guided portion 160 is made of a resin material.
Although the foregoing description has been made of the structure for housing the fan unit 110 in the fan unit mounting portion 120, structures for housing other electronic units in a unit mounting portion also have the same problem.